Mesoproterozoic Rocks and Cambrian Magmatism: How Rodinian Rifting Influenced Deposition of the Thickest, Most Porous and Permeable Unit in the Illinois Basin

Abstract

In the Illinois Basin, a section of the Cambrian-age Mt. Simon Sandstone referred to as the lower Mt. Simon is arguably the most important reservoir for fluid disposal and storage. Recent drilling has revealed the thickest section of the lower Mt. Simon at 600 feet with porosity ranging from 10 to 30% and permeabilities over a Darcy. With few holes penetrating this reservoir, the distribution across the basin is poorly constrained. Herein, we combine well logs, seismic reflection, and core data including detrital zircon age spectra to reconstruct the early Cambrian depositional and tectonic history of the Illinois Basin. Data reveal a complex tectonic history during the Mesoproterozoic through the early Cambrian leading to the incipient formation of this intracontinental basin and the deposition of the lower Mt. Simon Sandstone. Detrital zircon data confirms the existence of Mazatzal crust (~1660 Ma) beneath the Illinois Basin. Provenance of detrital grains is represented by (1) culminating stage of anorogenic magmatism associated with the Eastern Granite-Rhyolite province (1375 Ma), and (2) early Cambrian magmatism (530-540 Ma) that marked the final stages of the rifting of Rodinia. This new data is unique to the lower Mt. Simon Sandstone in the Illinois Basin and distinct from the overlying ubiquitous late Cambrian arenites present throughout the upper Midwest. When this exclusive provincial source is applied to Precambrian structure observed on seismic and well log data across the basin, the distribution of the lower Mt. Simon Sandstone reflected a northern arm of the Reelfoot Rift extended up into central Illinois.

AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019